Kinetics of furfural electrochemical hydrogenation and hydrogenolysis in acidic media on copper

May, Andrew S.; Watt, Steven; Biddinger, Elizabeth J.

doi:10.1039/d1re00216c

Cited by 22 publications

(59 citation statements)

References 34 publications

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“…Our results show that a decrease in pH promotes hydrogenolysis [i.e., the faradaic efficiency (FE) for DMF production increases from 1 to 28 % when the pH is lowered from 9 to 2] while suppressing hydrogenation. A similar trend has been observed for the reduction of furfural; [21][22][23] however, the reason for the observed pH dependence has not yet been elucidated in any of the prior studies. In this study, we computationally examined all possible HMF reduction pathways and the most feasible mechanistic routes [i.e., hydrogen atom transfer (HAT) and proton coupled electron transfer (PCET)] to form the intermediates for each of the pathways.…”

Section: Introductionsupporting

confidence: 69%

“…We note that a few studies have previously investigated electrochemical hydrogenation and hydrogenolysis mechanisms of simpler aldehydes like furfural and benzaldehyde [21,23,38,39] . However, no studies suggested the possibility that the hydrogenation and hydrogenolysis intermediates may require different hydrogenation (HAT vs. PCET) mechanisms.…”

Section: Resultsmentioning

confidence: 92%

“…We note that a few studies have previously investigated electrochemical hydrogenation and hydrogenolysis mecha- ChemSusChem nisms of simpler aldehydes like furfural and benzaldehyde. [21,23,38,39] However, no studies suggested the possibility that the hydrogenation and hydrogenolysis intermediates may require different hydrogenation (HAT vs. PCET) mechanisms. Our study for the first time shows that hydrogenation and hydrogenolysis involve the formation of different intermediates via different mechanisms (HAT vs. PCET), which makes it possible to explain why low pH can promote hydrogenolysis over hydrogenation.…”

Section: Computational Investigations On the Pathways For Dmfmentioning

confidence: 99%

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Mechanistic Differences between Electrochemical Hydrogenation and Hydrogenolysis of 5‐Hydroxymethylfurfural and Their pH Dependence

et al. 2022

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Hydrogenation and hydrogenolysis are two important reactions for electrochemical reductive valorization of biomass-derived oxygenates such as 5-hydroxymethylfurfural (HMF). In general, hydrogenolysis (which combines hydrogenation and deoxygenation) is more challenging than hydrogenation (which does not involve the cleavage of carbon-oxygen bonds). Thus, identifying factors and conditions that can promote hydrogenolysis is of great interest for reductive valorization of biomass-derived oxygenates. For the electrochemical reduction of HMF and its derivatives, it is known that aldehyde hydrogenation is not a part of aldehyde hydrogenolysis but rather a competing reaction; however, no atomic-level understanding is currently available to explain their electrochemical mechanistic differences. In this study, combined experimental and computa-tional investigations were performed using Cu electrodes to elucidate the key mechanistic differences between electrochemical hydrogenation and hydrogenolysis of HMF. The results revealed that hydrogenation and hydrogenolysis of HMF involve the formation of different surface-adsorbed intermediates via different reduction mechanisms and that lowering the pH promoted the formation of the intermediates required for aldehyde and alcohol hydrogenolysis. This study for the first time explains the origins of the experimentally observed pHdependent selectivities for hydrogenation and hydrogenolysis and offers a new mechanistic foundation upon which rational strategies to control electrochemical hydrogenation and hydrogenolysis can be developed.

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Section: Introductionsupporting

confidence: 69%

Section: Resultsmentioning

confidence: 92%

Section: Computational Investigations On the Pathways For Dmfmentioning

confidence: 99%

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Mechanistic Differences between Electrochemical Hydrogenation and Hydrogenolysis of 5‐Hydroxymethylfurfural and Their pH Dependence

et al. 2022

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“…Kinetic analysis of their reactions suggests that an Eley–Rideal-type mechanism is most likely operative in their system, which means the addition of hydrogen occurs by PCET. On the other hand, Biddinger and co-workers investigated the hydrogenation (production of furfuryl alcohol) and hydrogenolysis (production of methyl furan) of furfural in acidic media on Cu . The noncompetitive Langmuir–Hinshelwood mechanism was found to best fit their experimental data for both reactions, which means that the addition of H-atoms is achieved by HAT.…”

Section: Electrochemical Reductive Valorization Via Hydrogenation And...mentioning

confidence: 65%

Electrochemical Hydrogenation, Hydrogenolysis, and Dehydrogenation for Reductive and Oxidative Biomass Upgrading Using 5-Hydroxymethylfurfural as a Model System

et al. 2022

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Ever increasing energy demands and concerns about the environment necessitate the discovery of methods for producing fuels and chemicals from renewable resources in an environmentally benign manner. Electrochemical biomass conversion is particularly promising due to the abundance of renewable biomass and the advantages of electrochemistry, including the use of renewable electricity to drive chemical reactions without consumption of additional reductants and oxidants. Biomass intermediates are chemically complex and contain multiple functional groups, requiring selective reduction or oxidation for effective biomass conversion. Reductively, controlling the selectivity between hydrogenation and hydrogenolysis is necessary for efficient reduction of oxygenated functional groups to produce desired fuels and chemicals. Oxidatively, selective dehydrogenation of a particular functional group (e.g., alcohol or aldehyde oxidation to carboxylic acid) while preventing complete oxidation to CO2 is required for conversion of biomass to value-added products. In this Perspective, we use biomass-derived 5-hydroxymethylfurfural (HMF) as an especially useful model molecule for discussing recent developments in electrochemical hydrogenation, hydrogenolysis, and dehydrogenation reactions for biomass conversion, as HMF, which contains multiple functional groups, can be transformed into various valuable chemicals by both reductive and oxidative processes. For each reaction, the electrocatalysts, reaction conditions, and mechanisms will be discussed. Through this discussion, this Perspective aims to provide researchers with a foundational understanding of electrochemical hydrogenation, hydrogenolysis, and dehydrogenation reactions that can be applied to a wide variety of organic transformations, including biomass conversion.

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“…Recently, we conducted an initial rate study for FF ECH over Cu in acidic media to better understand the electrochemical kinetics. 29 This initial rate study avoided reaching significant concentrations of FA and MF, thereby mitigating the impact of the concentration-dependent undesired reactions onto the desired electrochemical kinetics. We found the FF ECH over Cu in acidic media followed a noncompetitive Langmuir−Hinshelwood model for both FA and MF, where FA and MF were produced via two different intermediate species.…”

Section: Introductionmentioning

confidence: 99%

Modeling Competing Kinetics between Electrochemical Reduction of Furfural on Copper and Homogeneous Side Reactions in Acid

May

Biddinger

2022

Energy Fuels

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The understanding of electrochemical reactions for the hydrogenation and hydrogenolysis (ECH) of biomass derived species is important to design and adapt electrochemical reactors to generate desired chemicals sustainably at high yield. In this work, the ECH of furfural (FF) over Cu foil catalysts to furfuryl alcohol (FA) and 2-methylfuran (MF) was studied in a twocompartment semibatch reactor in acidic electrolytes (0.1 and 0.5 M H 2 SO 4 ) with nitrogen sparging. We found that FA and MF underwent side reactions that follow first order kinetics with respect to the FA and MF concentrations in 0.1 M H 2 SO 4 and 0.5 M H 2 SO 4 . MF evaporation from the catholyte in the presence of nitrogen sparging followed a first order dependence with the concentration of MF in the catholyte. Our previous work showed the ECH of FF over Cu followed noncompetitive Langmuir−Hinshelwood models. A kinetic model was developed to consider the electrochemical reactions, nonelectrochemical side reactions, and the evaporation of MF to investigate the competition between these three contributions to the mass balances. Insights were provided by using the model to consider two hypothetical cases where 1) evaporation of MF did not occur, and 2) side reactions did not occur, and a third realistic case where evaporation of MF and side reactions occurred. The model showed that without gas sparging promoting MF evaporation, 81.5% of products were undesirable at 98.5% FF conversion in 0.5 M H 2 SO 4 , and 30.6% of products were undesirable in 0.1 M H 2 SO 4 . N 2 sparging in the catholyte lowered the concentration of MF in the catholyte with a corresponding increase to the concentration in the solvent trap, where side reactions did not occur, allowing for increased MF yields. We showed that despite the faster side reactions to MF in 0.5 M H 2 SO 4 compared to 0.1 M H 2 SO 4 , a higher yield to MF was reached in 0.5 M H 2 SO 4 than in 0.1 M H 2 SO 4 due to the beneficial impact of nitrogen sparging and the higher electrochemical production rate of MF.

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Kinetics of furfural electrochemical hydrogenation and hydrogenolysis in acidic media on copper

Abstract: Electrochemical processes can be implemented for the valorization of biomass-derived species such as furfural to generate fine chemicals and fuels. The electrochemical hydrogenation and hydrogenolysis (ECH) of furfural (FF) can...

Cited by 22 publications

References 34 publications

Mechanistic Differences between Electrochemical Hydrogenation and Hydrogenolysis of 5‐Hydroxymethylfurfural and Their pH Dependence

Mechanistic Differences between Electrochemical Hydrogenation and Hydrogenolysis of 5‐Hydroxymethylfurfural and Their pH Dependence

Electrochemical Hydrogenation, Hydrogenolysis, and Dehydrogenation for Reductive and Oxidative Biomass Upgrading Using 5-Hydroxymethylfurfural as a Model System

Modeling Competing Kinetics between Electrochemical Reduction of Furfural on Copper and Homogeneous Side Reactions in Acid

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